HIGHER HUMAN BIOLOGYUnit 2 Physiology and Health1. Ante-natal Screening

Recap• What are the two categories of contraception?• Give examples of physical methods?• What is the basis of chemical contraception?

What I need to know• What is the purpose of antenatal screening?• What are the two types of ultrasound scan?• What are dating scans and chemical tests used to

estimate?• What are anomaly scans used for?• What are biochemical tests and what are they for during

pregnancy?• Name two antenatal screening methods.• What are the advantages and disadvantages of the two

methods?• What is a karyotype and what are they used to

determine?• What is the Rhesus antibody and what are the risks

associated with this antigen during pregnancy?

What is the purpose of antenatal screening?

• Antenatal screening is carried out to monitor the health of a pregnant woman and her fetus

• Antenatal screening identifies the risk of a disorder so that further tests can be carried out and a prenatal diagnosis given

What are the two types of ultrasound scan?

• Dating scan • Anomaly Scan

What are dating scans used to determine?

• Carried out at 12 weeks

• Along with other chemical tests used to estimate how old the fetus is i.e. stage of pregnancy

• Also used to estimate the due date

What are anomaly scans used for? • Carried out at 20 weeks

• Used to determine any abnormalities in the development of the fetus

• Also used to estimate risk of Down’s Syndrome

Biochemical tests• Many physiological changes occur during pregnancy

• Biochemical tests are used to monitor these changes in order to highlight problems should they occur

Tests Include

Detect hypertension a pre-cursor to pre-eclampsia

• Blood analysis to detect blood type (Rhesus)

• Hormone concentrations (HCG)• Thyroid (hyperthyroidism) liver

and kidney function• Glucose analysis (gestational

diabetes)

False positives

• Human chorionic gonadotrophin levels in normal pregnancy

• HCG increases up to week 10 then decreases in normal pregnancy

• With a Down’s syndrome pregnancy HCG levels remain high throughout

• False positive results would be created if a blood sample was taken at week 10

Diagnostic Screening• These are procedures used to diagnose, without doubt, disorders associated with the developing fetus

• Offered if routine tests have highlighted problem or woman belongs to high risk category

• They include:• Amniocentesis• Chorionic villus sampling

Diagnostic testingAmniocentesis

• Carried out at 18 weeks• Less risk of miscarriage• Amniotic fluid removed• Karyotype produced• Decision to proceed/terminate

Chorionic villus sampling

• Carried out at 8 weeks• Higher risk of miscarriage• Placental cells removed• Karyotype produced• Decision to proceed/terminate

How tests are used – Assessing risk of Down’s syndrome

Step 1 – woman’s age/history

• Does she belong to high risk group

Step 2 – Blood analysis

• Alpha-fetoprotein concentration

• Levels are normal if within 0.5 – 2.49

• Low levels (less than 0.4) can indicate high risk of Down’s syndrome

• Baby may not have Down’s syndrome even in high risk

How tests used – Down’s syndrome diagnosisStep 3a –Amniocentesis offered

• If high risk indicated amniocentesis is offered to confirm diagnosis

Step 3b – Nuchal translucency

Rhesus Antibody

Blood test Analysis

• Mother Rhesus negative (no antigen for rhesus on her blood cells)

• Causes problems if she is carrying a Rhesus positive baby

• Mother becomes sensitised after birth and produces Rhesus antibodies

Second pregnancy

• If the baby is Rhesus positive

• Rhesus antibodies from mother cross placenta and attack red blood cells

• Baby born severely anaemic• Prevention – Rhesus

negative expectant mothers given Rhesus antibody injections

Activities• Make notes, summary on ante-natal screening

procedures

• Testing your Knowledge Qs• p146 No’s 1-4